Traditional methods of cross-breeding plants have been used to introduce desirable genetic traits from one plant to another, and the production of so-called hybrid seeds is crucial to the agricultural industry. However, in order to obtain hybrid seeds, the self-pollination of a plant must be prevented.
Pollen production can be prevented by applying to the plant or soil a chemical composition such as those disclosed in U.S. Pat. No. 4,801,326 issued to Ackmann et al. A preferred use of such compounds is to apply them 2-4 times at intervals of 3 to 10 days in order to maximize inhibition of pollen production in the female plants. Hybrid seeds are then produced by the cross fertilization of the female plants by pollen from adjoining rows of non-treated plants. Although this method may prevent pollen production, it is labor-intensive and may require close attention to the developmental stage of the plants for timely application of the chemical composition. In addition, this method presents potential problems with toxicity of chemicals introduced into the environment.
Some plants, such as corn and sugar beet, contain a cytoplasmic gene(s) for male sterility which results in the absence of pollen production. U.S. Pat. No. 3,861,079 (Patterson) discloses procedures for using inbred lines of maize carrying male sterile genes. However, the presence of certain cytoplasmic male sterility genes is accompanied by a sensitivity to certain fungal pathogens, and for many plants cytoplasmic male sterility genes are not available.
A method of inhibiting pollen production without relying on endogenous plant genes or application of chemicals to crops or to soil would be very beneficial to the agricultural industry. By using genetic manipulation techniques to insert a gene which will inhibit only pollen production into the genome of a plant, reliance on naturally occurring male sterility genes will be unnecessary.
The use of a plant promoter and an exogenous gene to effect changes in the genetic make-up of plants is known, in the art. European Patent Application No. 0122791 (Hall et al.) discloses the use of a DNA shuttle vector comprising T-DNA and a plant structural gene. The specific application disclosed by Hall et al. is to enhance protein content and nutritional value of crops such as alfalfa by causing expression of the gene for the seed storage protein phaseolin. T-DNA is used because it can be stably integrated into transformed plant cell genomes. European Pat. Application No. 0126546 (Kemp et al.) discloses the enhancement of the protein content of crops by using a plant structural gene in combination with a T-DNA promoter instead of the plant promoter for that particular structural gene. U.K. Patent Application No. 2,187,462 (Marcker et al.) discloses the use of a root nodule promoter with root nodule-specific genes or other genes to establish nitrogen-fixing capacity in non-leguminous plants and to add new traits, such as resistance to herbicides, diseases and pests. Such promoters are only functional in root nodules. The Hall and Kemp patents teach the use of T-DNA as the vector for incorporating a promoter and structural gene into the plant genome. In each case the utility requires the expression of the structural gene associated with either the plant promoter or the T-DNA promoter. These patents do not teach the use of pollen-specific promoters to initiate transcription and translation of either endogenous or exogenous genes.
A need thus exists for a method of inducing male sterility in plants without relying on traditional breeding methods or on applications of chemicals to plants or soil.